The present invention includes methods, devices, and systems suited to the receiving and transmitting of wide color gamut image and video data. Such data can be transmitted between devices of a multi-media network. Such networks can include audio-video source devices (example audio-video source devices including, but not limited to cameras, video recorders, set-top boxes, DVD players, Blu-ray Disc players, personal computers (PCs), video game consoles (e.g., PlayStation 3, Wii, and Xbox 360, etc.)) and audio-video sink devices (examples including digital audio-video devices, computer monitors, digital televisions, convertor boxes, display devices, and AV receivers of many different varieties).
One of the current issues in the communication of color data is the sheer number of existing color formats, color spaces, and color gamut's used to generate, transmit, and display image data. In many such formats there is very little commonality between the formats. Accordingly, conversions must be made between the formats to render the resultant images in a faithful manner. In many cases, due to the many inherent difficulties in converting between formats (for example, the various HD and SD formats), the conversion is simply not performed at all. This results in a wide range of distortions and deviations from the intended color gamut resulting in a significantly distorted image as finally displayed.
The inventors point out that the use of standardized formats (examples including, but not limited to, sRGB, scRGB, an Adobe RGB, DCI-P3, SMPTE-C, ITU_R.BT601 (CCIR601), ITU_R.BT709, xvYCC, and grey-scale formats, as well as others) results in compromises in color fidelity. For example, each device has its own range of color capability defining a unique color gamut for that device. For example, a video recording device or other image capture device has a certain range of sensitivity to color and brightness that is generally unique to that device. This is represented as a “native” color gamut for such a device. One problem with the standardized color formats is that they have a defined color range over which the device can operate. This range will impose limits on the devices and resultant image fidelity where the standard format does not coincide with the native format of the device (in nearly 100% of cases).
Using FIG. 1(a) as an example, a simplified depiction of a number of different color spaces is shown. Here, a graph 100 figuratively represents a chromaticity diagram showing a CIE 1931 color space 111, an sRGB color space 101, and a wide color gamut space scRGB 112. Additionally, a “native” image capture color gamut 102 for an example image capture device (such as a camera) is depicted in dashed line. It is to be noted that certain regions 103 of the native color gamut 102 cannot be represented by the sRGB color space. Accordingly, distortions occur when the image data captured by the image capture device is encoded. Commonly, areas like that of 103 are simply lost in the conversion to a standard format.
In addition, referring to FIG. 1(b), when a captured image is displayed on a monitor having a smaller color gamut than that represented by the input data (i.e., the input data can defines a range of color and brightness beyond the capabilities of the monitor) an out of gamut problem will occur for those colors having no analog in the color space of the display device. For example, display gamut 111 is not able to display the full color range of an input image 112. The portions of the image 112 not realizable using a display with color gamut 111 are “out of gamut” 113. Numerous approaches for dealing with this problem can be used. In one common mode, out of gamut clipping will occur and the regions 113 are merely “clipped” from the image data and represented by some color at the edge of the color space 111. It can easily be seen that many conversions to standard formats (for example, sRGB) result in lost data and the inability to capture the full color gamut of an originating device. Thus, a first level of distortion is introduced into the image data. However, for many purposes, clipping and other color distortions associated with mapping to a standardized format are acceptable.
Additionally, image data encoded in one format may not be able to take full advantage of the large color gamut's available from modern sink devices. In such cases portions of the display gamut extend beyond a standard color space (e.g., an sRGB color space). Accordingly, the expanded color gamut available in a wide gamut sink device (e.g. a display) cannot be exploited by merely displaying an ordinary sRGB encoded image signal. In some cases, a reference gamut can be used to map image data to a wider gamut. For example, sRGB data can be mapped to a wider gamut format, such as an scRGB to obtain an expanded color gamut for display. However, due to peculiarities of the mapping algorithms, distortions also occur when the image data is mapped in this way. Moreover, there is no guarantee that the mapped data will look anything like the original data captured with an originating image capture device.
Thus, even though existing color formats are useful for many purposes, they lack the ability to take full advantage of the color capability of modern display and image content generation devices. Additionally, existing formats do not have the ability to adapt to the myriad of different color gamut's available in modern multi-media device (e.g., AV (audio-video) devices). There are many situations where higher colorimetric range and/or fidelity are desirable. There are also situations where a system needs to be flexible enough to capture many different color gamut's such as are present in the vast array of devices available today. The present invention addresses these concerns and provides methods and devices capable of providing enhanced color gamut support with relatively low system overhead. In facilitating this invention, the inventors have conceived of methods and devices that enable the transmission and receipt of color image and video data between devices. Importantly, the approach disclosed by the inventors has a number of desirable features. For one, the approaches discussed here feature wide color gamut support, a flexible and adaptable approach, and a relatively small amount of data overhead. These and other features of the inventions are highly useful and are described herein.